1. Field of the Invention
The present invention relates to a screwed pipe connection for connecting a pipeline having a nominal outer cross-section, a nominal inner cross-section, a nominal wall thickness, and a connection end with a wall region formed by shaping.
These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:
These and other features and advantages of the present invention will become more readily appreciated when considered in connection with the following detailed description and appended drawings, wherein:
Furthermore, the invention relates to a method for producing a screwed pipe joint, in particular a screwed pipe joint of the type described above, wherein a wall region of a connection end of a pipeline is subject to reshaping and with the application of force in axial direction of the pipeline inside a mold of a tool, an outer contour of the connection end is formed.
2. Description of Related Technology
From the international standard ISO 8434-1, screw joints are known that are used for the sealed connection of a pipe to a pipe-connection part or a screw-in part. In this standard, so-called 24° cone connectors of various designs are described. These connections comprise a connection part and a union joint part that can be screwed into the connection part for sealed retention of the pipeline, wherein the connection part has a receiving opening with an inner conical bore that widens outward in the direction of the pipeline, and wherein the connection end of the pipeline can be inserted in a positive and/or force-fitting manner between the connection part and the union joint part. The angle designation of 24° refers here to the opening angle of the inner conical bore of the connection part, which widens outward in the direction of the pipeline and is embodied in particular as a tapered bore.
One type of embodiments according to the standard ISO 8434-1 has screw joints that are produced in each case using a cutting ring. As is known, such a cutting ring is an annular part located on the outer circumference of the pipeline that clamps the pipeline in a positive and/or force-fitting manner at its connection end, between the connection piece and the union joint part. On the side facing the connecting part, the cutting ring has a cutting section with at least one cutting edge which, when the union joint part is tightened, is pushed due to the effect of the conical bore of the connection part axially toward the connection part and which, at the same time, cuts radially into the wall of the pipe to be connected. Here, the cross-section of the connection end of the pipeline—except for a small region that is deformed by the cutting edge—is embodied in the same manner as the rest of the pipe body, in particular in respect of its inner and outer diameter; thus, it has the same diameter.
Screw connections comprising cutting rings of various designs are also known from DE-AS 1 167 608, DE-AS 1 175 639, GB 1 117 987 A, U.S. Pat. No. 2,406,488 A and EP 1 776 539 B1 and have long been a standard in fluid technology. The advantages of such connections are low system costs for screw-connection components and machines, the short minimum distance to a pipe bend required when making the connections, which allows for a compact design and the possibility of direct assembly inside the screw connection without the use of assembly machinery. It is considered disadvantageous that the proper handling of the cutting-ring systems during pre- and final assembly requires technical knowledge and experience, that the quality of an achieved preassembly result can only be partially verified, that the cutting rings have difficulty cutting into high-strength steels, and that after a preassembly of the cutting ring, gaps often appear between the cutting ring and the pipe due to elastic deflection of the ring, which gaps must be closed during final assembly.
In addition to the screw joints described above, such screw connections are also known from the international standard ISO 8434-2, where the connection part does not have a conical bore widening outward in the direction of the pipeline but rather an outer conical bore that tapers inward. In particular, in ISO 8434-2, this is a flanged 37° cone connector, wherein the pipeline can be inserted with its connection end that is flanged outwardly in a positive manner by means of an annular cuff-part between the connection part and the union joint part. The inner surface of the flanged pipe-end region abuts the complementary-shaped outer side of the outer bore of the connection part. The angle designation here refers to the opening angle of the outer bore of the connection part, which tapers inward in the direction of the pipeline. This system is also called a JIC system. Whereas with the 24° systems according to ISO 8434-1, an axially induced assembly force is amplified into a clamping and sealing force acting against the cone plane that is approximately 4.8 times normal, in the case of the 37° systems according to ISO 8434-2, an axially induced clamping and sealing assembly-force acting against the cone plane is amplified to only about 1.7 times normal. Thus, compared to 24° cone connectors, the 37° cone connectors have fundamental disadvantages with regard to tightness and assembly behavior.
Screw pipe connections for connecting prefabricated pipelines that have in each case, at their connection ends, a toroidal bulge formed by a compression-reshaping process, are known in numerous embodiments, and devices for producing said screw pipe connections are normally referred to as pipe-forming systems. In these pipelines, proceeding from an end face of the connection end facing the connection part in a first longitudinal section, an outer diameter of the pipeline formed by the reshaped wall area of the connection end increases in axial direction, becoming larger than the nominal outer diameter, and then, in a second longitudinal section, decreasing again in axial direction, until it reaches the nominal outer diameter behind the connection end. The changes in cross-section may occur progressively or suddenly, whereas in the latter case, the second longitudinal section is nearly zero. For the purpose of example only, with respect to the type and production of such screw connections, reference is made to the publications DE 195 20 099 C2, DE 195 26 316 C2 and EP 1 054 203 A1.
Screwed pipe joints designed in this way normally have great installation height, because they require long straight clamping lengths up to the pipe bend for reshaping of the connection end for the pipe. In these regions, it is a disadvantage that insertion can also result in damage to an anticorrosion coating of the pipeline, if such a coating is present. Furthermore, the metal-forming machine tools are often expensive, because they must be designed to produce very considerable forces (for example 1,000 kN with a pipe diameter of 42 mm).
With such screwed pipe joints, there is also a major disadvantage in that during assembly, when tightening the screwed connection (union nut), the pipe tends to revolve along with the nut. This disadvantage is eliminated by a screwed pipe joint as described in EP 1 260 750 B1. In this screwed joint, a support ring is provided, it being possible to clamp the pipeline with its toroidal bulge and the screwed connection in a positive manner between the connection piece—called the coupling connection in the cited document—and the support ring located on the pipeline between the toroidal bulge and the screwed connection. The support ring, with the toroidal bulge, forms a specially designed contact surface, in the region of which, when tightening the screwed joint, essentially no radial force components occur.
The cited screwed pipe joints have stood the test of use. With them, in addition to the advantage of there being a possibility to employ a soft seal at the pipe end, there is also the possibility of checking, in a simple manner, in the preassembly results, the quality of the bead contour produced, and there can subsequently be reliable final assembly characterized by the following advantageous features:                there is already direct contact between pipe and coupling cone during manual tightening of the screwed connection;        assembly can be performed with low tightening torque up to a stop position;        the system is uncritical to over- and under-tightening.        
In order to produce contoured pipe ends of this or a similar kind, which particularly in the tapering longitudinal region are provided with a corresponding bulge contour, a device for plastically deforming tool elements, as described in EP 1 494 827 B1, can be used. Such a device has a molding assembly actuated by the pressure of a fluid and a pre-tensioning unit that is actuated by a fluid pressure, particularly a hydraulic pressure, the two units being arranged on a common longitudinal axis, as well as tensioning elements that are tensible by means of the pre-tensioning unit. Here, for reshaping, a toolkit is required that is comprised, in addition to the tensioning elements, of a molding head, by means of which the contour is formed at the pipe end through an axial compression process. This is therefore a method of the type referred to at the beginning.
The problem, which forms the basis of the invention, consists of making a screwed pipe joint of the type referred to at the beginning and a method for its production, which is characterized by a guarantee of high static and dynamic resilience of the screwed pipe joint due to reduced installation height and improved resistance to corrosion, or as the case may be by less complex and expensive mechanical production, and which avoids the disadvantages of the prior art described above.